• Gary W. Kronk's Comets & Meteor Showers: C/1999 S4 (LINEAR)
  • Nederlandse kometenvereniging: 1999S4 (LINEAR)
  • Sky&Telescope, November 1999: New Comet LINEAR


    NASA Headquarters, Washington, DC
    Goddard Space Flight Center, Greenbelt, MD
    Space Telescope Science Institute, Baltimore, MD

    August 7, 2000

    HUBBLE DISCOVERS MISSING PIECES OF COMET LINEAR

    To the surprise and delight of astronomers, NASA's Hubble Space Telescope has discovered a small armada of "mini-comets" left behind by what some astronomers had assumed was a total disintegration of the explosive comet LINEAR.

    Hubble's powerful vision has settled the fate of the mysteriously-vanished solid nucleus of the comet, which seemed to disappear after it moved around the Sun.

    On July 27, ground-based observers lost sight of the bright core of the comet and suggested that the nucleus disintegrated into a pile of dust. Astronomers at the Space Telescope Science Institute (STScI) in Baltimore, MD, quickly reprogrammed Hubble to search for the missing nucleus. Johns Hopkins University astronomer Hal Weaver said he was stunned when the Hubble image popped up on his computer screen. "My first thought was Hubble Space Telescope does it again! We caught the fish! This is amazing, very exciting, very neat."

    Though comets have been known to break apart before, this is the first time astronomers have a close-up view of the dismantling of a comet's nucleus due to the Sun's heat. Since the 1950s, researchers assumed comet nuclei were loose clusters of ice and dust, called cometesimals, held together by gravity. Solar heat causes the ices to sublimate and violently release gas as explosions and garden hose-style jets. The pressure of the solar radiation blows away particles like debris caught in a gale.

    Some astronomers think that the fragments now being seen in LINEAR may be the primordial building blocks of the original nucleus, the so-called cometesimals, which theory predicts should be several tens of feet across. The breakup of a comet tells scientists how it was put together in the first place. The cometesimals were built up from micron-sized grains of dust as it collected in the early solar system, roughly 4.6 billion years ago.

    On Weaver's screen were at least a half dozen "mini-comets" with tails, resembling the shower of glowing fireballs from fireworks. They were clustered in the lance-head tip of an elongated stream of dust and an isolated brighter piece in front of the cluster may be the parent nucleus for the smaller fragments. Hubble's exceptional resolution and sensitivity allowed it to reveal the nuclei as separated bodies at a level of detail never before seen in a disintegrating comet.

    Some astronomers find it hard to imagine how an object the size of a mountain could totally disintegrate in only two weeks. "Actually, I would have been more amazed if Hubble saw no pieces," adds co-investigator Carey Lisse, of STScI. "The comet's breakup was too violent and fast for it to completely vaporize. How do you pulverize something the size of a mountain?"

    Weaver says it will be important for the largest ground-based telescopes to try and see the mini-comets as they spread apart. This may yield further clues on the structure of the original nucleus and the sizes of the remaining fragments.

    Some astronomers believe this was Comet LINEAR's first visit to the inner solar system, after traveling for nearly the distance of one light-year (six trillion miles) from the vast comet storehouse called the Oort cloud. Other astronomers suggest that LINEAR may have been a fragile piece that broke off of a larger comet that visited our solar system more than 10 million years ago.

    It's estimated that 20-30 percent of comets are so fragile they completely disintegrate when they pass the Sun.

    The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract with NASA's Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA).

    Electronic image files.


    Space Weather News for August 4, 2000

    Comet LINEAR blew apart so thoroughly last week that astronomers can't find any sizable pieces from its fractured icy core. New groundbased images of the comet posted today revealed no fragments brighter than 22nd magnitude. The new data are fueling speculation that Comet LINEAR itself might have been the fragment of a larger body that passed through the inner solar system centuries ago.

    For more information please visit SpaceWeather.com


    ISAAC NEWTON GROUP OF TELESCOPES
    Roque de Los Muchachos Observatory, La Palma

    4 August 2000

    COMET LINEAR: GOING, GOING... BUT NOT QUITE GONE !

    Continuous monitoring of Comet LINEAR by the Jacobus Kapteyn Telescope showed that it was disintegrating as it approached the Sun. The latest and best images from the larger aperture Isaac Newton Telescope now give us the clearest idea so far of how and why the comet disintegrated.

    Having previously appeared completely normal, on the night of July 25th the comet was seen to undergo a rapid change. The initially compact comet nucleus evolved into a fuzzy, extended and much fainter object. This caused much speculation as to what the reason for the disruption of the comet might be. Further observations with the telescopes of the Isaac Newton Group at the Roque de los Muchachos Observatory, La Palma, Spain as well as telescopes elsewhere have confirmed the initial discovery and provided new insight into what the reason for the comet disruption could be: the evaporation of all the ice in the nucleus.

    Cometary nuclei are a mixture of solid lumps of material of various sizes, held together by a cement of ices. When comets pass close to the Sun during their journey across the solar system the icy elements (mainly water ice and carbon monoxide ice) sublime, leaving loose material behind that forms the dust tail of the comet, while the sublimed ice forms its gas tails. As a result of this process, or due to the strong gravitational pull from a planet such as Jupiter, or from the Sun, a comet nucleus may sometimes split into two or more fragments. What was seen in the case of Comet LINEAR, however, was different.

    From analysis of the images that lay out the recent sequence of events for Comet LINEAR, Dr. Mark Kidger from the Spanish Instituto de Astrofisica de Canarias concludes that this small comet probably ran out of ice altogether, leaving behind a loose conglomerate of particles that are now gradually dispersing into space. This model fits the observations well, as measurements have shown that the activity of the comet had been declining for several weeks as ice gradually sublimed away. During the comet's closest approach to the Sun, a burst of activity was recorded. Then, when all the ice was exhausted and nothing was holding together the solids, the nucleus began to fall apart.

    The latest images taken with the 2.5 metre Isaac Newton Telescope after break-up show no sign of the comet's original nucleus, nor of any active sub-nuclei larger than a few metres across. Any large remnants of the nucleus that remain cannot be subliming significantly or they would have been detected in these images. This corroborates the sequence of events proposed by Dr. Kidger. Other comets are known to have disappeared, but Comet LINEAR is the first one to have been caught in the act.

    Comet LINEAR has maybe not been a spectacular night-time sight for most people, but for astronomers it presents an important and unique event of what can be described as the death of a comet.

    The Isaac Newton Group of telescopes (ING) is an establishment of the Particle Physics and Astronomy Research Council (PPARC) of the United Kingdom and the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) of the Netherlands. The ING operates the 4.2 metre William Herschel Telescope, the 2.5 metre Isaac Newton Telescope, and the 1.0 metre Jacobus Kapteyn Telescope. The telescopes are located in the Spanish Observatorio del Roque de Los Muchachos on La Palma which is operated by the Instituto de Astrofisica de Canarias (IAC).

    PICTURES

    Picture 1:

    Close view of the coma

    Caption: This image, obtained on 1 August, is a 100-second exposure with the Wide Field Camera of the 2.5 metre Isaac Newton Telescope. This section of the full image measures 4.5 arcminutes, equivalent to 110,000 km at the comet. This image is processed to show faint details in the coma of the comet. This is by far the best and deepest image of the broken-up nucleus that exists and gives us a clear idea of how and why the comet disintegrated. No features are seen in the image, which implies that no significant individual fragments more than a few metres across still emit gas. This demonstrates the catastrophic disruption of the nucleus. Unlike comet Shoemaker-Levy 9, the only remnant that remains is an expanding dust cloud.

    Picture 2:

    Comet Linear's tail

    This image, obtained on 1 August with the Wide Field Camera of the 2.5 metre Isaac Newton Telescope, covers a field of view of 22 arcminutes and is processed to show the faint tail of the comet, which extends well beyond the edge of the field of view.

    Picture credit: Dr. Mark Kidger, Instituto de Astrofisica de Canarias

    Picture 3:

    Isaac Newton Telescope

    The 2.5 metre Isaac Newton Telescope. Picture credit: Nik Szymanek and Ian King.


    Meltdown!

    Comet LINEAR continues to disintegrate and could disappear completely within a few days.

    NASA Science News

    July 31, 2000 -- Astronomers around the world continue to monitor the unexpected disintegration of comet C/1999 S4 (LINEAR). Intense solar heating apparently triggered a massive disruption of the comet's fragile icy core when it passed close to the Sun last week. It is still bright enough to see through small telescopes so even amateur astronomers can watch the comet as it dissolves. If you do plan to look, don't wait. Experts think that comet LINEAR might disappear completely in a few days.

    The break up of a bright comet is unusual but not unprecedented. For example, comet Shoemaker-Levy 9 (SL-9) broke up before it struck Jupiter in 1994. SL-9 was discovered after it fragmented, so there is no record of what happened as it came to pieces. With comet LINEAR, astronomers have a ringside seat for the entire show.

    "We have observed a few comets in the process of breaking up -- comet West in 1976, comet Ikeya-Seki in 1965 and others -- but never with so much detail as we're seeing in comet LINEAR," says Mark Kidger, an astronomer at the Instituto de Astrofisica de Canarias. Comet LINEAR's demise seems to be a bit unusual. "Cometary splittings rarely ever lead to the rapid disappearance of a comet like this - in fact, I don't know of another case"

    Kidger was the first to notice comet LINEAR disintegrating as he monitored a cloud of gas (called the "coma") surrounding the comet's core using the 1-meter Jacobus Kapteyn Telescope. Comet LINEAR, which has been falling toward the Sun since it was discovered in September 1999, made its closest approach to our star (perihelion) on July 26, 2000. Perihelion is a critical time for any comet. It's when solar heating of the icy core is most intense and when the comet swings around for its long return trip to the outer solar system.

    "At perihelion there are very rapid aspect changes as regions of the nucleus previously in shadow are suddenly subjected to intense heating," continued Kidger. "This causes strong thermal stresses" that may have been a primary cause of LINEAR's breakup.

    Something was already amiss the day before Comet LINEAR reached perihelion at a distance of 114 million km (0.74 AU) from the Sun.

    "The very first images on July 25th were enough to show me that something odd was going on," recounts Kidger. "The comet's inner coma was no longer teardrop-shaped (the solar wind flowing around the comet's head causes this shape). It had a shape like a short, fat cigar. My first thought was 'Shoemaker-Levy.' It looked just like those first images of Comet Shoemaker-Levy 9 after it was discovered."

    Kidger's images on subsequent nights confirmed that something dramatic was happening and he announced his findings in an International Astronomical Union (IAU) Circular (IAUC #7467) on July 27, 2000. As news of the breakup spread, astronomers around the world trained their telescopes on the comet. In another IAU Circular (IAUC # 7468) published July 28th, three teams of observers reported that they too saw evidence of a major event in the comet's nucleus.

    Unlike comet Shoemaker-Levy 9, which broke into many well-defined bright fragments, comet LINEAR seems to be dissolving into an amorphous haze of gas and dust.

    "There is some similarity of appearance to the two comets," says Brian Marsden of Harvard's Minor Planet Center. "An observation by Ian Griffin in New Zealand on July 29th shows the nucleus of C/1999 S4 (LINEAR) extended into a long, bright string. However, it does not seem to show discrete nuclei in that string, as D/1993 F2 (SL-9) did."

    The differences between comets SL-9 and LINEAR result from their different sizes and distances from the Sun.

    Comet Shoemaker-Levy 9 was larger than comet LINEAR, and it broke apart as the result of tidal stresses it experienced when it passed less than 100 thousand kilometers from Jupiter (within 1.4 Jupiter radii from the planet's center). SL-9 was far from the Sun (812 million km) when it fragmented and solar heating was not the primary cause of the break up. In fact, SL-9 wasn't even orbiting the Sun. The comet had been captured by the gravitational pull of Jupiter and was orbiting the giant planet instead.

    Comet LINEAR is a much smaller object that has been losing mass rapidly during its approach to the Sun. The Hubble Space Telescope recorded a house-sized fragment blowing away from the core on July 5th and powerful jets of gas vaporized by solar radiation have been pushing the comet to and fro. Solar heating is a more important factor in its breakup than gravitational effects.

    "The small size of comet LINEAR and its exposure to solar radiation is causing a more complete and rapid dissolution than we saw in Shoemaker-Levy 9," continued Marsden. "The initial break-up of SL-9 was surely caused by tidal forces from Jupiter. If they had not later collided with Jupiter, several of those fragments would presumably still exist. C/1999 S4 (LINEAR), on the other hand, will probably have completely dispersed in a week or so."

    Comet LINEAR may still be bright enough for amateur astronomers to view in small telescopes, but it's fading fast. On July 27th, binocular observers in South America and Europe estimated the comet's visual magnitude to be +6.6. That's almost bright enough to see with the unaided eye from dark-sky observing sites. Two days later, an experienced amateur in the Canary Islands reported a visual magnitude of +8.3, a factor of 6 decline in brightness.

    "The surface brightness of the innermost coma is fading fast," says Kidger. "This should translate to a somewhat slower fade of the outer coma [that binocular and small telescope observers see] as the gas and dust in it disperses and is not replenished. Typically a comet may take several weeks for the coma to expand and fade down to the brightness of the sky background."

    Many well-known annual meteor showers, including the Perseids, Leonids and Geminids, are caused by dusty debris from comets burning up in the atmosphere of Earth. Such displays are harmless and beautiful. Unfortunately for meteor lovers, the orbit of comet LINEAR comes no closer to our planet than 28 million kilometers (0.18 AU). There will be no "Linearid" meteor shower. When comet LINEAR finally disappears from view in a few days or weeks, this memorable visitor from beyond the orbit of Neptune will be gone forever.


    Space Weather News for July 28, 2000

    There is growing evidence that comet LINEAR, which made its closest approach to the Sun earlier this week, is disintegrating. Today's spaceweather.com features images and animations of the apparent breakup.

    Also, an interplanetary shock wave struck Earth's magnetosphere on July 28, 2000, triggering minor geomagnetic activity.

    For more information please visit SpaceWeather.com


    NASA Science News for July 28, 2000

    Although comet LINEAR was not bright enough to see with the unaided eye when it passed by Earth this week, the comet is grabbing the attention of astronomers with peculiar behavior, including orbit-altering jets and fragments breaking away from its nucleus.

    Full story.


    NEWSALERT: Friday, July 28, 2000 @ 1431 GMT

    The latest news from Astronomy Now and Spaceflight Now

    DEATH OF A COMET: LINEAR BLOWN APART

    Astronomers report that Comet LINEAR, the brightest comet of the year, appears to have blown apart. The comet, which at one time was predicted to become visible to the naked eye, dramatically faded this week.

    Full story.

    NASA OBSERVATORIES KEEP THEIR 'EYES' ON LINEAR

    When NASA's two great observatories, Hubble and Chandra, recently observed comet LINEAR astronomers received some abrupt surprises. Researchers were able to catch the icy comet in a brief, violent outburst when it blew off a piece of its crust, like a cork popping off a champagne bottle.

    Full story.


    ISAAC NEWTON GROUP OF TELESCOPES
    Roque de Los Muchachos Observatory, La Palma

    Friday 28 July 2000

    THE JACOBUS KAPTEYN TELESCOPE OBSERVES THE DEATH OF COMET LINEAR

    Nightly observations made since July 23 in different broadband filters with the 1-m Jacobus Kapteyn Telescope on La Palma, Canary Islands, Spain show what appears to be the complete disruption of the nucleus of comet LINEAR, the brightest comet of the year.

    Dr. Mark Kidger, Instituto de Astrofisica de Canarias reports from the Jacobus Kapteyn Telescope: "The central condensation was highly condensed and showed the typical 'teardrop' form in the evening of July 23rd and July 24th, although its brightness decreased by a factor of about 3 between the two nights. In the evening of July 25th something very odd was happening to the comet: the central condensation was seen to be strongly elongated, with a very flat brightness distribution. The condensation's brightness faded further and its length increased on the following nights. On July 27 there was no evidence of any local brightness peaks that would indicate the presence of sub-nuclei."

    In other words, it does not appear to have broken into individual fragments in the way that Comet Shoemaker-Levy 9 did in 1993. Instead, it has completely blown apart.

    The expansion velocity of the condensation is about 40 m/s, indicating that it is solid particles and not gas. The gas tail, which virtually disappeared between July 23rd and 24th, has reformed as an extension of the major axis of the central condensation.

    Comet LINEAR, or C/1999 S4 (LINEAR) as it is called in correct astronomical nomenclature, is a by-product of the automated LINEAR minor-planet survey. Discovered nearly as far out as Jupiter last September, this comet passed 114 million kilometres from the Sun on July 26 and only 56 million kilometres from Earth on July 22. Comet LINEAR is a "new" comet which means that it is making its very first passage through the inner solar system. The surfaces of new comets are believed to be covered almost completely by a very thin, fragile layer of highly volatile ices such as carbon dioxide intermixed with dust.

    When discovered, Comet LINEAR was immediately regarded as a candidate likely to reach naked eye visibility based on its relative brightness and large heliocentric distance. New comets though are notoriously difficult to predict as far as their light curve behaviour is concerned, particularly many months in advance.

    At present Comet LINEAR is diving southward from the constellation Ursa Major into Leo. It will be about 20 degrees above the west-northwest horizon as evening twilight deepens. Although not visible to the naked eye, the comet will continue to be in northern skies until the second week of August, when it will dip below the horizon. The observations with the Jacobus Kapteyn Telescope suggest though that the comet is dying very quickly and may disappear completely within a few days.

    The Jacobus Kapteyn Telescope will continue to observe its disintegration over the next few nights, hopefully giving new insights into the nature of comet nuclei and their structure.

    The Jacobus Kapteyn Telescope is part of the Isaac Newton Group of Telescopes (ING). The ING is an establishment of the Particle Physics and Astronomy Research Council (PPARC) of the United Kingdom and the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) of the Netherlands. Apart from the Jacobus Kapteyn Telescope, the ING also operates the 4.2 metre William Herschel Telescope and the 2.5 metre Isaac Newton Telescope. The telescopes are located in the Spanish Observatorio del Roque de Los Muchachos on La Palma which is operated by the Instituto de Astrofisica de Canarias (IAC).

    PICTURES

    Disruption of the nucleus of Comet LINEAR

    Caption: An image of the nucleus of Comet LINEAR as seen on the Jacobus Kapteyn Telescope on July 26th. This is the raw, unprocessed image that the astronomer saw straight off the telescope. The unusual elongated shape was the first evidence of the comet's complete break-up.

    Picture credit: Dr. Mark Kidger, Instituto de Astrofisica de Canarias.

    The Jacobus Kapteyn Telescope

    Caption: The 1-m Jacobus Kapteyn Telescope.

    Picture credit: Nik Szymanek and Ian King.

    More information on ING:

    http://www.ing.iac.es/PR/
    http://www.ast.cam.ac.uk/ING/PR/

    More information on this news can be found in IAU Circular 7467.

    Other web sites:

    Mark Kidger's comet web pages<
    Comet LINEAR's web pages


    JULY 28, 2000

    Space Telescope Science Institute, Baltimore, MD
    Johns Hopkins University, Baltimore, MD

    HUBBLE SEES COMET LINEAR BLOW ITS TOP

    Using NASA's Hubble Space Telescope, researchers were surprised to catch the comet LINEAR (C/1999 S4) in a brief, violent outburst when it blew off a piece of its crust, like a cork popping off a champagne bottle. The eruption, the comet's equivalent of a volcanic explosion (though temperatures are far below freezing, at about minus 100 degrees Fahrenheit in the icy regions of the nucleus or core), spewed a great deal of dust into space. This mist of dust reflected sunlight, dramatically increasing the comet's brightness over several hours. Hubble's sharp vision recorded the entire event and even snapped a picture of the chunk of material jettisoned from the nucleus and floating away along the comet's tail.


    NASA Headquarters, Washington, DC
    Space Telescope Science Institute, Baltimore, MD
    Johns Hopkins University, Baltimore, MD
    Goddard Space Flight Center, Greenbelt, MD
    Marshall Space Flight Center, Huntsville, AL
    Chandra X-ray Observatory Center, Harvard-Smithsonian Center for Astrophysics, Cambridge, MA

    July 27, 2000

    NASA'S TWO GREAT OBSERVATORIES KEEP THEIR "EYES" ON COMET LINEAR

    When NASA's two great observatories, the Hubble Space Telescope and the Chandra X-ray observatory, recently observed comet LINEAR (C/1999 S4) astronomers received some abrupt surprises.

    Using the Hubble Space Telescope, researchers were surprised to catch the icy comet in a brief, violent outburst when it blew off a piece of its crust, like a cork popping off a champagne bottle.

    The eruption, the comet's equivalent of a volcanic explosion -- though temperatures are far below freezing (about minus 100 degrees Fahrenheit or minus 40 degrees Celsius) in the icy regions of the nucleus or core -- spewed a great deal of dust into space. This mist of dust reflected sunlight, dramatically increasing the comet's brightness over several hours. Hubble's sharp vision recorded the entire event and even snapped a picture of the chunk of material jettisoned from the nucleus and floating away along the comet's tail.

    "We lucked out completely," said Hubble comet-watcher Harold Weaver of the Johns Hopkins University, Baltimore, MD. "In one surge of brilliance this under-performing comet showed us what it could have been. Comet LINEAR generally has not been as bright as we had hoped, but occasionally does something exciting."

    Though comet nuclei have been known to fragment, Hubble's sharp vision is revealing finer details of how they break apart. This unexpected glimpse at a transitory event may indicate that these types of "Mt. Saint Helens" outbursts occur frequently on the comet, because it is unlikely that Hubble just happened to catch one isolated event, Weaver said.

    The orbiting observatory's Space Telescope Imaging Spectrograph tracked the streaking comet for two days, July 5 to 7, capturing the leap in brightness and discovering the castaway chunk of material sailing along its tail. When the Hubble telescope first spied the comet 74 million miles (120 million km) from Earth, it watched the icy object's brightness rise by about 50 percent in less than four hours. By the next day, the comet was a third less luminous than it had been the previous day. On the final day, the comet was back to normal.

    During the outburst's peak, the astronomers believe that the comet jettisoned the piece of its crust seen days later in the tail. The renegade fragment moved away from the core's weak gravitational grasp at an average speed of about six miles per hour, which is a little more than a brisk walking pace.

    A week later, on July 14, NASA's Chandra X-ray Observatory imaged the comet and detected X-rays from oxygen and nitrogen ions. The details of the X-ray emission, as recorded on Chandra's Advanced CCD Imaging Spectrometer (ACIS), show that the X-rays are produced by collisions of ions racing away from the Sun with gas in the comet.

    "This observation solves one mystery. It proves how comets produce X-rays," said Carey Lisse of the Space Telescope Science Institute, Baltimore, MD, leader of a team of scientists from the institute; NASA's Goddard Space Flight Center, Greenbelt, MD; Johns Hopkins; the University of California, Berkeley; and the Harvard-Smithsonian Center for Astrophysics, Cambridge, MA. "With an instrument like Chandra, we can now study the chemistry of the solar wind and observe the X-ray glow of the atmosphere of comets, as well as other planets such as Venus."

    Comet LINEAR was named for the observatory that originally discovered it in September 1999. LINEAR is the acronym for Lincoln Near Earth Asteroid Research, a project operated by the Massachusetts Institute of Technology's Lincoln Laboratory, Lexington, MA, to search for Earth-approaching objects.

    The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract with Goddard Space Flight Center. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency.

    Chandra's ACIS instrument was built for NASA by the Massachusetts Institute of Technology, Cambridge, and Pennsylvania State University, University Park. NASA's Marshall Space Flight Center, Huntsville, AL, manages the Chandra program. The Smithsonian's Chandra X-ray Observatory Center controls science and flight operations from Cambridge, MA.

    Images associated with this release are available on the Internet at:

    http://oposite.stsci.edu/pubinfo/pr/2000/26

    Chandra images are available at:

    http://chandra.harvard.edu


    Space Weather News for July 22, 2000

    Comet LINEAR will reach maximum brightness around July 23, 2000, as it glides past the bowl of the Big Dipper. Sky watchers have been hoping that LINEAR would become visible to the unaided eye. However, monitoring data from a global network of astronomers suggest that the comet's brightness will peak at a visual magnitude of +6.5, just below the threshold for naked-eye visibility. LINEAR should still be a visual treat when viewed through binoculars or a small telescope.

    For more information please visit SpaceWeather.com NOTE to readers: Since SpaceWeather.com was launched in its current form on January 1, 2000, the site has focused on solar and geomagnetic activity. Comets and meteors are an important aspect of space weather, too. With today's update about comet LINEAR we will begin an accelerating program of coverage for comets, meteor showers, and related astronomical events.


    =====================================================================
               SKY & TELESCOPE'S NEWS BULLETIN - AUGUIST 4, 2000
    =====================================================================
    For images and Web links for these items, visit http://www.skypub.com
    =====================================================================
    

    COMET LINEAR (C/1999 S4) This summer's well-known cometary visitor is having its last gasp and has all but disappeared from view. On July 24th the cometís strongly condensed nucleus began to elongate, and its brightness diminished dramatically. Most likely, the comet broke apart as it approached its July 26th perihelion, when it was closest (114 million kilometers) to the Sun. At that time the nucleus would have undergone incredible thermal stress, and it appears Comet LINEAR buckled and disintegrated under the intense heat. This week astronomers plan to use the Hubble Space Telescope to look for fragments of the disrupted nucleus. Meanwhile, for telescopic observers here on Earth, the comet has begun to move south and had faded to below 9th magnitude.

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    Comet LINEAR Bright Enough For Binoculars

    By Jeff Kanipe
    space.com

    23 June 2000

    A comet heading for the inner solar system may not fulfill expectations of being bright enough to be seen with the naked eye, but astronomers are at least sure of one thing: it will be the brightest comet since Hale-Bopp graced the heavens three years ago. You can add another thing. It should be bright enough to seen with binoculars.

    The new comet goes by the mumbo-jumbo name of 1999 S4 LINEAR, an acronym which stands for Lincoln Laboratory Near-Earth Asteroid Research -- an automated-search program in New Mexico that images regions of the night sky looking for asteroids and comets. This one was found in digital images made on September 27 and was reported, at the time, as "an unusual moving object."

    Full story here.


    space.com

    Icy visitor may become visible to naked eye

    By Jeff Kanipe

    June 6, 2000

    The buzz among amateur astronomers for the last several months concerns a comet that may reach naked-eye brightness in mid July. Comet 1999 S4 LINEAR (named after Lincoln Laboratory Near Earth Asteroid Research, an automated program that images regions of the night sky looking for asteroids and comets) may reach anywhere between magnitudes 3 and 5 or 6 around July 19-25.

    Although not a blockbuster by any means, it's still potentially the brightest comet we've had since Hale-Bopp's momentous apparition three years ago.

    Comet LINEAR may hover between magnitude 5 and 6 until early August. Right now, it's a small, magnitude-10 fluff of light within the constellation Triangulum in the predawn sky. A 4-inch (10-centimeter) telescope and low magnification should be able to detect it. You might even try binoculars.

    Full story here.


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